1. Field of the Invention
This invention relates generally to an electronic imaging camera with increased dynamic range and, more particularly, to an electronic imaging camera in which the effective dynamic range of the light detecting array is substantially increased.
2. Description of the Prior Art
Electronic imaging cameras for recording still images are well known in the art. Such cameras can record a plurality of still images on a single magnetic disk or tape in either analog or digital format for subsequent playback on any well-known cathode ray tube (CRT) viewing device. Printers may also be utilized with such cameras in a well-known manner to provide hard copy of the recorded images. Such electronic imaging still cameras may also utilize two-dimensional image light sensing arrays such as charge coupled devices (CCD's) which integrate incident scene light over a predetermined time to provide an electronic information signal corresponding to the scene light intensities incident to the array.
Electronic imaging cameras of the aforementioned type also commonly employ electronic viewfinders where the scene is sensed in ambient scene light by the image sensing array at standard video rates, where each field is sensed for 1/60th of a second. Thus, the incident scene light for each frame is integrated for 1/60th of a second to provide the video electronic information signal to the electronic viewfinder display. High resolution solid state image sensing devices such as the aforementioned charge coupled device have relatively limited dynamic exposure ranges resulting from the individual picture elements or pixels of the charge coupled device saturating under conditions of high intensity incident scene illumination and incurring low signal to noise ratios under conditions of low intensity incident scene illumination. The dynamic exposure range for such solid state image sensing arrays is quite limited and substantially less than the dynamic exposure range of most photographic films. Thus, full advantage cannot be taken of the wide dynamic illumination range of typical outdoor scenes in view of the limited dynamic exposure range of the image sensing array.
In addition such cameras may also use an electronic flash to provide full artificial illumination under conditions of low ambient scene light, or partial fill-in artificial illumination under conditions of high ambient scene light intensity where the subject may be backlit or shadowed. Under conditions where an electronic flash is utilized to provide supplemental illumination to fill in and properly expose a central subject, the reflected artificial illumination is ordinarily sensed by a photodetector control circuit to terminate the light integration when the central subject is properly exposed. This exposure time may not be sufficient to properly expose the background, particularly outdoors where the background of the scene is likely to be located far beyond the range of the electronic flash. However, since the exposure times during the aforementioned preview mode of operation are at standard video rates, the background of the scene may be better exposed than during the shorter period of light integration as occurs during the firing of a flash of artificial illumination as a result of the rapid falloff of the flash illumination with increasing distance.
Therefore, it is a primary object of this invention to provide an electronic imaging still camera in which the effective dynamic exposure range of the image sensing array is substantially expanded.
It is a further object of this invention to provide an electronic imaging camera in which the dynamic exposure range of the image sensing array is substantially expanded by discriminating between the electronic information signals derived from at least two successive exposure intervals defined by different exposure limiting parameters.
It is an even further object of this invention to provide an electronic imaging still camera in which the electronic information signal ultimately recorded corresponding to a desired scene is derived as a function of two different succeeding exposure intervals.
It is an even further object of this invention to provide an electronic imaging still camera in which a still image is ultimately recorded as a function of the scene light detected during a first exposure interval in which the scene light is not artificially illuminated and a second exposure interval illuminated by a flash of artificial illumination.
Other objects of the invention will be in part obvious and will in part appear hereinafter. The invention accordingly comprises a mechanism and system possessing the construction, combination of elements and arrangement of parts which are exemplified in the following detailed disclosure.